The Space Flight System (or SLS) rocket’s first launch has been postponed by NASA once again because engineers were unable to stop a persistent hydrogen leak.

This morning, just as the rocket was about to be fuelled with liquid hydrogen, a leak of hydrogen was discovered. As fuel was being transferred to the rocket, a leak “formed on the supply side of the 8-inch fast disconnect,” according to NASA. The team tried three different troubleshooting techniques, but each time they tried to repair the issue, a leak was found. Engineers advised against the launch after the third attempt. Charlie Blackwell-Thompson, the mission’s launch director, made the decision to abort the launch attempt shortly after.

One of the mainstays of NASA’s Artemis program is the SLS. It is responsible for launching the unmanned Orion crew capsule around the Moon for this mission, known as Artemis I. NASA’s next missions will try to use SLS, Orion, and more tools to get people back to the lunar surface.

In addition, the agency postponed the SLS’s last launch attempt that was scheduled for August 29 due to problems with the engine bleed system, which is intended to let the engines reach the right temperature before takeoff. Additionally, a hydrogen leak was discovered during that failed launch.

Before a significant delay, NASA has one more launch window remaining on September 5th, from 5:12 to 6:42 PM. The flight termination system, which is intended to prevent the rocket from turning into a dangerous missile in the event that something goes drastically wrong during launch, needs to be retested fairly frequently (it was originally supposed to be every 20 days, but NASA successfully lobbied to extend that to every 25 days), and testing cannot be done on the launch pad.

After September 5th, NASA’s time will essentially be up since the rocket rolled out to the launch pad on August 16. The SLS will need to be wheeled back to NASA’s Vehicle Assembly Building so that the termination system can be tested again if it doesn’t launch at that time. That will take time, maybe delaying this debut until no later than the end of October.

However, if that launch is successful, it should open the door for a mission next year when NASA will send a crew into space for the first time in the Orion capsule. They won’t be landing on the moon; that milestone is set for 2025, when we expect to witness the first woman walk on the moon. Instead, they’ll simply be flying around it.